what family does this specimen belong to?
It has a plumose antenna, but I don't dare to say if its ending is forked or not. Doesn't look like Drosophilidae to me, so I give it a try with Periscelidae.
Length 2,5mm, found in Vienna on May 22nd.

Found the walking behaviour interesting: instead of moving forward, most of the time it walked sideways in some sort of 'gliding' movement.

This is a Stenomicridae! Judging on the black bands on the hind femora and tibia Stenomicra soniae.
Did you collect the specimen? And can you tell something about the habitat and/or plant you caught it in/on?